As a needle thread passing device of such a type, one disclosed in Patent Documents 1 (Japanese Patent No. 3,315,364) is known. In this needle thread passing device, a needle insertion cylinder having a bottomed needle insertion hole is placed upright on a main body having a pedestal surface, and a thread passing hole to be communicated with a needle eye of an inserted needle is formed in a lower portion of the needle insertion cylinder in a direction crossing the needle insertion hole. A thread placement portion is formed near the entrance of the thread passing hole, and a thread locking piece is provided at an operating member provided in the main body. The thread locking piece is configured to be freely inserted into and removed from the thread passing hole through the operating member by a pressing force of a pressing member provided in the main body. In this configuration, a needle is inserted into the needle insertion hole of the needle insertion cylinder, a thread is set at the thread placement portion, and the pressing member is pressed. Then, the operating member is swung. As a result, the thread locking piece provided in the operating member pulls the thread set at the thread placement portion into the thread passing hole, whereby the thread is inserted into the needle eye. When the pressing force of the pressing member is released, the operating member swung back by a spring to its original position. As a result, the thread is passed through the needle eye.
Patent Documents 1: Japanese Patent No. 3315364